Molybdenum (iv) amide precursors and use thereof in atomic layer deposition

ABSTRACT

Molybdenum (IV) amide complexes are disclosed herein corresponding in structure to Formula (I): wherein: L is —NR 1 R 2 ; R 1  and R 2  are C 1 -C 6 -alkyl or hydrogen; R is C 1 -C 6 -alkyl; and n is zero, 1, 2 or 3. Further, methods of forming MoO 2  films by atomic layer deposition (ALD) using Formula (I) complexes and Mo[N(Me)(Et)] 4  are disclosed herein.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority to U.S. Patent Application Ser. No.61/377,692 filed on 27 Aug. 2010, the entire disclosure of which isincorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to molybdenum (Mo) (IV) amide precursorsand methods of preparing MoO₂ films by atomic layer deposition (ALD)using such precursors.

BACKGROUND OF THE INVENTION

ALD is a known method for the deposition of thin films. It is aself-limiting, sequential unique film growth technique based on surfacereactions that can provide atomic layer control and deposit conformalthin films of materials provided by precursors onto substrates ofvarying compositions. In ALD, the precursors are separated during thereaction. The first precursor is passed over the substrate producing amonolayer on the substrate. Any excess unreacted precursor is pumped outof the reaction chamber. A second precursor is then passed over thesubstrate and reacts with the first precursor, forming a monolayer offilm on the substrate surface. This cycle is repeated to create a filmof desired thickness.

ALD processes have applications in nanotechnology and fabrication ofsemiconductor devices such as capacitor electrodes, gate electrodes,adhesive diffusion barriers and integrated circuits. Further, dielectricthin films having high dielectric constants (permittivities) arenecessary in many sub-areas of microelectronics and optelectronics. Thecontinual decrease in the size of microelectronics components hasincreased the need for the use of such dielectric films.

Green, J., et al. report the synthesis and isolation of the Mo complex,Mo(C₅H₅)(NMe₂)₃ . J. Chem. Soc., Dalton Trans., 1997, Pages 3219-3224.

U.S. Pat. No. 5,064,686 reports a Mo (IV) complex for use in chemicalvapor deposition (CVD). Mo[N(Me)(Me)]₄ was attempted in CVD. However,issues with thermal stability were noted in CVD and it has been foundthat although this precursor is similar in structure, it is not suitablefor depositing a MoO₂ layer.

Further, it was found that Mo(NtBu)₂(NMe₂)₂ did not work well forforming MoO₂ films by ALD because it formed MoO₃ films which isunsuitable for DRAM. Therefore a need exists to discover new Moprecursors which are capable of depositing MoO₂ films by ALD, which haveimproved thermal stability, higher volatility or increased depositionrates.

SUMMARY OF THE INVENTION

In one embodiment, a complex corresponding in structure to Formula I

is provided wherein L is —NR¹R²; R¹ and R² are C₁-C₆-alkyl or hydrogen;R is C₁-C₆-alkyl; and n is zero, 1, 2 or 3.

In another embodiment, a method of forming a MoO₂ film by ALD isprovided. The method comprises delivering at least one precursor to asubstrate, wherein the at least one precursor corresponds in structureto Formula I above.

In another embodiment, the complex Mo[N(Me)(Et)]₄ is provided and itsuse in ALD to form MoO₂ films.

Other embodiments, including particular aspects of the embodimentssummarized above, will be evident from the detailed description thatfollows.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a graphical representation of thermogravimetric analysis (TGA)data demonstrating mg vs. temperature/time of Mo[N(Me)(Et)]₄.

DETAILED DESCRIPTION OF THE INVENTION

In various aspects of the invention, Mo (IV) amide precursors areprovided and methods of use thereof are provided to form MoO₂ films byALD.

In one embodiment, the methods of the invention can be used to create orgrow Mo-containing thin films which display high dielectric constants. Adielectric thin film as used herein refers to a thin film having a highpermittivity.

As used herein, the term “precursor” refers to an organometallicmolecule, complex and/or compound which is delivered to a substrate fordeposition to form a thin film by ALD.

The term “Cp” refers to a cyclopentadienyl (C₅H₅) ligand which is boundto a transition metal. As used herein, all five carbon atoms of the Cpligand are bound to the metal center in η⁵-coordination by π bonding,therefore the precursors of the invention are π complexes.

The term “alkyl” refers to a saturated hydrocarbon chain of 1 to about 6carbon atoms in length, such as, but not limited to, methyl, ethyl,propyl and butyl. The alkyl group may be straight-chain orbranched-chain. For example, as used herein, propyl encompasses bothn-propyl and iso-propyl; butyl encompasses n-butyl, sec-butyl, iso-butyland tert-butyl. Further, as used herein, “Me” refers to methyl, and “Et”refers to ethyl.

The term “amino” herein refers to an optionally substituted monovalentnitrogen atom (i.e., —NR¹R², where R¹ and R² can be the same ordifferent). Examples of amino groups encompassed by the inventioninclude but are not limited to

Further, the nitrogen atom of this amino group is covalently bonded tothe metal center which together may be referred to as an “amide” group(i.e.

This can be further referred to as an “ammono” group or inorganic amide.

In a first embodiment, a “pianostool” complex corresponding in structureto Formula I

is provided wherein: L is —NR¹R²; R¹ and R² are independentlyC₁-C₆-alkyl or hydrogen; R is C₁-C₆-alkyl; and n is zero, 1, 2 or 3.

R¹ and R² can be the same or different. In a particular embodiment, bothR¹ and R² are methyl. In another particular embodiment, R¹ is methyl andR² is ethyl.

In a further embodiment, when n is zero, R¹ and R² are different fromeach other.

In one embodiment, R¹ and R² are independently methyl, ethyl or propyl;R is methyl, ethyl or propyl; and n is zero, 1 or 2.

In another embodiment, R¹ and R² are the same; R is methyl; n is zero, 1or 2.

In another embodiment, R¹ is methyl and R² is ethyl; R is methyl; and nis zero, 1 or 2.

Examples of complexes corresponding in structure to Formula I is

(cyclopentadienyl)Mo(NMe₂)₃;

(methylcyclopentadienyl)Mo(NMe₂)₃;

(ethylcyclopentadienyl)Mo(NMe₂)₃;

(propylcyclopentadienyl)Mo(NMe₂)₃;

(methylcyclopentadienyl)Mo(NEt₂)₃;

(ethylcyclopentadienyl)Mo(NEt₂)₃;

(propylcyclopentadienyl)MoNEt₂)₃;

(cyclopentadienyl)Mo(NMeEt)₃;

(methylcyclopentadienyl)Mo(NMeEt)₃;

(ethylcyclopentadienyl)Mo(NMeEt)₃; and

(propylcyclopentadienyl)Mo(NMeEt)₃.

In another embodiment, the cyclopentadienyl ring on the Mo (IV) amidecomplex is replaced with another amide group to form a tetrakisamide:Mo[N(Me)(Et)]₄.

The complexes according to Formula I and Mo[N(Me)(Et)]₄ are used asprecursors to form MoO₂ films by ALD. The precursors disclosed hereinmay be delivered for deposition to a substrate in pulses alternatingwith pulses of an appropriate oxygen source, such as H₂O, H₂O₂, O₂,ozone, iPrOH, tBuOH or N₂O.

In one embodiment a MoO₂ film can be formed by delivering for depositionat least one precursor according to Formula I, independently or incombination with a co-reactant. Examples of such co-reactants include,but are not limited to hydrogen, hydrogen plasma, oxygen, air, water,H₂O₂, ammonia, hydrazines, alkylhydrazines, boranes, silanes, ozone orany combination thereof.

A variety of substrates can be used in the methods of the presentinvention. For example, the precursors according to Formula I orMo[N(Me)(Et)]₄ may be delivered for deposition on substrates such as,but not limited to, silicon, silicon oxide, silicon nitride, tantalum,tantalum nitride, or copper.

The ALD methods of the invention encompass various types of ALDprocesses. For example, in one embodiment conventional ALD is used toform a metal-containing film of the invention. For conventional and/orpulsed injection ALD process see for example, George S. M., et. al. J.Phys. Chem. 1996. 100:13121-13131.

In another embodiment, liquid injection ALD is used to form ametal-containing film, wherein a liquid precursor is delivered to thereaction chamber by direct liquid injection as opposed to vapor draw bya bubbler (conventional). For liquid injection ALD process see, forexample, Potter R. J., et. al. Chem. Vap. Deposition. 2005. 11(3):159.

Examples of liquid injection ALD growth conditions include, but are notlimited to:

(1) Substrate temperature: 160-300° C. on Si(100)

(2) Evaporator temperature range: about 120-200° C.

(3) Reactor pressure range: about 2-50 mbar

(4) Solvent: toluene, or any solvent mentioned above

(5) Solution concentration Range: about 0.05 to 2 M

(6) Injection rate range: about 1-100 pulse⁻¹ (4 pulses cycle⁻¹)

(7) Inert gas flow rate: about 50-500 cm³ min⁻¹

(8) Pulse sequence (sec.) (precursor/purge/H₂O/purge): will varyaccording to chamber size.

(9) Number of cycles: will vary according to desired film thickness.

The precursor may be dissolved in an appropriate hydrocarbon or aminesolvent. Appropriate hydrocarbon solvents include, but are not limitedto aliphatic hydrocarbons, such as hexane, heptane and nonane; aromatichydrocarbons, such as toluene and xylene; aliphatic and cyclic ethers,such as diglyme, triglyme and tetraglyme. Examples of appropriate aminesolvents include, without limitation, octylamine andN,N-dimethyldodecylamine. For example, the precursor may be dissolved intoluene to yield a 0.05 to 1M solution.

In another embodiment, at least one precursor corresponding in structureto Formula I and/or Mo[N(Me)(Et)]₄ may be delivered “neat” (undiluted bya carrier gas) to the substrate.

In another embodiment, photo-assisted ALD is used to form ametal-containing film. For photo-assisted ALD processes see, forexample, U.S. Pat. No. 4,581,249.

In another embodiment, both liquid injection and photo-assisted ALD maybe used to form a metal-containing film using at least one precursorcorresponding in structure to Formula I and/or Mo[N(Me)(Et)]₄.

In another embodiment, plasma-assisted ALD may be used to form ametal-containing film using at least one precursor corresponding instructure to Formula I and/or Mo [N(Me) (Et)]₄.

Thus, the organometallic precursors corresponding in structure toFormula I and Mo[N(Me)(Et)]₄ utilized in these methods may be liquid,solid, or gaseous. Particularly, the precursors are liquid at ambienttemperatures with high vapor pressure for consistent transport of thevapor to the process chamber.

ALD relies substantially on chemical reactivity and not thermaldecomposition. Therefore, there are fundamental differences in thecharacteristics desirable for a suitable precursor. The precursor mustbe thermally stable at the temperatures employed and should besufficiently volatile to allow deposition onto the substrate. Further,when depositing a metal oxide film, a fast and complete chemicalreaction is necessary between the metal precursor and the oxide source.However the reaction should only take place at the substrate surface soas not to damage the underlying structure and by-products, such ascarbon and hydrogen, should be removed readily from the surface.

It has been discovered that variation of the substitution of the Cp ringand three identical ligands attached to the metal center demonstratesuseful and improved properties for ALD processes. For example, theprecursors of Formula I provide an increased ability to deposit MoO₂films by ALD at growth rates approaching that for simple metal amidesbut can operate at higher temperatures due to increased thermalstability which leads to improved product quality. Moreover, the use ofMo(IV) amide pianostool-type complexes enhances ALD performance bypolarizing the molecule to allow reaction with the surface which can besaturative to self-limit film growth for excellent conformal control.

In particular embodiments, the methods of the invention are utilized forapplications such as dynamic random access memory (DRAM) andcomplementary metal oxide semi-conductor (CMOS) for memory and logicapplications, on substrates such as silicon chips.

In a further embodiment, a method is provided for forming a “mixed”metal film by ALD. The term “mixed” metal film as used herein is toindicate that at least two different metals comprise the film.

In one embodiment, a mixed-metal film is formed by ALD by delivering fordeposition at least one precursor according to Formula I and/orMo[N(Me)(Et)]₄ and at least one co-precursor having a different metalcenter. For example, at least one Mo precursor according to Formula Iand/or Mo[N(Me)(Et)]₄ and at least one appropriate co-precursor, such asa lead, titanium, strontium and/or barium precursor may be delivered fordeposition to a substrate to create a mixed-metal film.

A thin film created by a method of the invention can have a permittivityof between 10 and 250, preferably at least 25 to 40 and more preferablyat least 40 to 100. Further, an ultra high permittivity can beconsidered to be a value higher than 100. It is understood by one ofordinary skill in the art that the resulting permittivity of the filmdepends on a number of factors, such as the metal(s) used fordeposition, the thickness of the film created, the parameters andsubstrate employed during growth and subsequent processing.

EXAMPLES

The following examples are merely illustrative, and do not limit thisdisclosure in any way. All manipulations were carried out in an inertatmosphere using a glove box and Schlenk line techniques. NMR analysiswas carried out using a Bruker 250 MHz machine.

Example 1 Synthesis of Mo(NMeEt)₄

Lithium N-ethyl,methylamide was prepared using standard techniques from^(n)BuLi and HNEtMe. To ^(n)BuLi (680 ml, 1.6M in hexanes, cooled to 0°C. with ice bath) was added drop-wise over a period of 4 hoursN-ethylmethylamine (65.6 g, 1.1 moles). The mixture was allowed to warmto room temperature once all the amine had been added and was thenstirred overnight. To this was added THF (250 ml) and the mixturestirred for 1 hour and then cooled to 0° C. in an ice bath. To thismixture was added MoCl₅ (50.2 g, 0.18 moles, added in small portions of˜1-2 g over a period of 8 hrs due to large exotherm and spitting ofmixture). The dark brown (almost black) reaction mixture was allowed towarm to room temperature once all the MoCl₅ had been added and was thenrefluxed for 1 hour. The mixture was cooled and then stirred overnight.The mixture was allowed to settle (LiCl) and filtered using standardtechnique. Solvent was stripped from the reaction mixture and then thepurple liquid sublimed/distilled out of the reaction mixture to yield apurple liquid.

Distillation conditions: pressure in the range 3.5×10⁻² Torr and oilbath temperature 100-110° C.

Mo(NEtMe)₄ NMR δ, ppm - (integrations) Assignment 1.17 (12 H) Ethyl CH₃,i.e. NCH₂ CH ₃ 3.22 (8 H) Ethyl CH₂, i.e. N CH ₂ CH₃ 3.49 (12 H) Methylon nitrogen, i.e. N CH ₃

FIG. 1 displays TGA data for Mo(NMeEt)₄.

Example 2 Synthesis of [Mo(MeCp)(NEtMe)₃]

To a dark purple toluene solution (60 ml) of Mo(NEtMe)₄ (prepared above,3.3 g, 0.01 moles) cooled to 0° C. in an ice bath was added freshlycracked MeCpH (4 g, 0.05 moles, added via syringe). No immediate colourchange was observed and so the mixture was allowed to stir at roomtemperature for 2 hrs. Again no colour changes were observed and so themixture was refluxed for 3 hrs to produce a dark green solution. Thetoluene was stripped form the reaction mixture to yield a dark greenliquid.

Mo(^(Me)Cp)(NEtMe)₃ 1.00, (9 H) Ethyl CH₃, i.e. CH₂ CH ₃ 1.60, (3 H)Methyl group on Cp ring, i.e. Me Cp 2.95, (9 H) Methyl on nitrogen, i.e.N CH ₃ 3.15, (6 H) Ethyl CH₂, i.e. N CH ₂ CH₃ 4.95 (2 H) Cp ringHydrogen 5.15, (2 H) Cp ring Hydrogen

Example 3 ALD using [Mo(MeCp)(NEtMe)₃]

MoO₂ films are deposited in a custom-built ALD reactor. Mo(MeCp)(NEtMe)₃and ozone are used as precursors. The MoO₂ films are deposited onsilicon wafer substrates. Prior to deposition, the wafer substrates areprepared by dicing the wafer (1 inch×½ inch), and 1% HF polish.

The growth temperature is 200-350° C. The growth pressure is 0.5-1.5Torr. The reactor is continuously purged with 30 sccm of dry nitrogen.All the computer controlled valves in the reactor are the air operatedALD VCR valves from Cajon.

Ozone is purged in excess. The molybdenum is stored in a stainless steelampoule. Attached directly to the ampoule is an ALD valve. The output ofthis ALD valve is Tee'd with another ALD valve used for nitrogeninjection. The Tee outlet leg is connected to a 500 cm³ stainless steelreservoir. The outlet of the reservoir is attached to a third ALD valve,called the inject valve, whose outlet goes directly to the reactor.Nitrogen injection is used to build up the total pressure behind themolybdenum inject valve so that the pressure is higher than the reactorgrowth pressure. The injected nitrogen is accomplished using a 30 micronpin hole VCR gasket. All of the valves and ampoule are placed into anoven-like enclosure that allows the ampoule, valves, and tubing to beheated uniformly to 50° C. to 250° C.

During the ALD growth operation, the valves are sequenced in thefollowing manner. The molybdenum precursor is introduced to theactivated silicon surface. A nitrogen purge then takes place whichincludes evacuation to remove surplus reactant molecules not attached tothe surface. Ozone is then introduced followed by an additional purgewith nitrogen. The ozone is then injected to start the ALD cycle allover again.

The total amount of cycles is typically 300.

All patents and publications cited herein are incorporated by referenceinto this application in their entirety.

The words “comprise”, “comprises”, and “comprising” are to beinterpreted inclusively rather than exclusively.

What is claimed is:
 1. The complex Mo[N(Me)(Et)]₄.
 2. A method offorming a MoO₂ film by atomic layer deposition, the method comprisingdelivering Mo[N(Me)(Et)]₄ to a substrate.
 3. A Mo(IV) complexcorresponding in structure to Formula I

wherein: L is —NR¹R²; R¹ and R² are independently C₁-C₆-alkyl orhydrogen; R is C₁-C₆-alkyl; and n is zero, 1, 2 or 3, wherein when n iszero, R¹ and R² are different from each other.
 4. The complex of claim3, wherein R¹ and R² are independently methyl, ethyl or propyl; R ismethyl, ethyl or propyl; and n is zero, 1 or
 2. 5. The complex of claim3, wherein R¹ and R² are the same; R is methyl; and n is zero, 1 or 2.6. The complex of claim 3, wherein R¹ is methyl and R² is ethyl; R ismethyl; and n is zero, 1 or
 2. 7. The complex of claim 3, wherein thecomplex corresponding in structure to Formula I is selected from thegroup consisting of: (methylcyclopentadienyl)Mo(NMe₂)₃;(ethylcyclopentadienyl)Mo(NMe₂)₃; (propylcyclopentadienyl)Mo(NMe₂)₃;(methylcyclopentadienyl)Mo(NEt₂)₃; (ethylcyclopentadienyl)Mo(NEt₂)₃;(propylcyclopentadienyl)MoNEt₂)₃; (cyclopentadienyl)Mo(NMeEt)₃;(methylcyclopentadienyl)Mo(NMeEt)₃; (ethylcyclopentadienyl)Mo(NMeEt)₃;and (propylcyclopentadienyl)Mo(NMeEt)₃.
 8. The complex of claim 3,wherein the complex corresponding in structure to Formula I is selectedfrom the group consisting of: (methylcyclopentadienyl)Mo(NMe₂)₃;(methylcyclopentadienyl)Mo(NMeEt)₃; and (cyclopentadienyl)Mo(NMeEt)₃. 9.A method of forming a MoO₂ film by atomic layer deposition, the methodcomprising delivering at least one precursor to a substrate, wherein theat least one precursor corresponds in structure to Formula I:

wherein: L is —NR¹R²; R¹ and R² are independently C₁-C₆-alkyl orhydrogen; R is C₁-C₆-alkyl; and n is zero, 1, 2 or
 3. 10. The method ofclaim 9, wherein R¹ and R² are independently methyl, ethyl or propyl; Ris methyl, ethyl or propyl; and n is zero, 1 or
 2. 11. The method ofclaim 9, wherein R¹ and R² are the same; R is methyl; and n is zero, 1or
 2. 12. The method of claim 9, wherein R¹ is methyl and R² is ethyl; Ris methyl; and n is zero, 1 or
 2. 13. The method of claim 9, wherein theat least one precursor corresponding in structure to Formula I isselected from the group consisting of: (cyclopentadienyl)Mo(NMe₂)₃;(methylcyclopentadienyl)Mo(NMe₂)₃; (ethylcyclopentadienyl)Mo(NMe₂)₃;(propylcyclopentadienyl)Mo(NMe₂)₃; (methylcyclopentadienyl)Mo(NEt₂)₃;(ethylcyclopentadienyl)Mo(NEt₂)₃; (propylcyclopentadienyl)MoNEt₂)₃;(cyclopentadienyl)Mo(NMeEt)₃; (methylcyclopentadienyl)Mo(NMeEt)₃;(ethylcyclopentadienyl)Mo(NMeEt)₃; and(propylcyclopentadienyl)Mo(NMeEt)₃.
 14. The method of claim 9, whereinthe at least one precursor corresponding in structure to Formula I isselected from the group consisting of:(methylcyclopentadienyl)Mo(NMe₂)₃; (methylcyclopentadienyl)Mo(NMeEt)₃;(cyclopentadienyl)Mo(NMeEt)₃; and (cyclopentadienyl)Mo(NMe₂)₃.
 15. Themethod of claim 9, wherein the atomic layer deposition is selected fromthe group consisting of photo-assisted atomic layer deposition, liquidinjection atomic layer deposition and plasma-assisted atomic layerdeposition.
 16. The method of claim 9, wherein the precursor isdeposited onto the substrate in pulses alternating with pulses of anoxygen source selected from H₂O; H₂O₂; O₂; ozone; iPrOH; tBuOH and N₂O.17. The method of claim 9, wherein at least two precursors correspondingin structure to Formula I are delivered to the substrate to form a MoO₂film by atomic layer deposition.
 18. The method of claim 9, furthercomprising delivering to the substrate at least one co-precursor to forma mixed-metal film by atomic layer deposition.
 19. The method of claim9, wherein the at least one precursor corresponding in structure toFormula I is dissolved in a solvent prior to delivery to the substrate.20. The method of claim 19, wherein the at least one precursorcorresponding in structure to Formula I is delivered neat to thesubstrate.
 21. The method of claim 9, wherein the MoO₂ film is used fora memory and/or logic application.